Most sources of energy today are objectionable in that they pollute the atmosphere. When fuel is combusted in an internal combustion engine or for a gas turbine or a furnace which is used to produce steam, the combustion products are often objectionable in that they contain large amounts of pollutants. Among the pollutants are the gases which are oxides of nitrogen. Such gases are recognized as being hazardous to health and harmful to the environment.
In order to convert as much heat to useful energy as possible, combustion air is usually kept to a minimum to limit the amount of exhaust gas produced and therefore the heat lost in the escaping gas. This makes for a very high combustion temperature.
It is recognized that the oxides of nitrogen are produced from combustion air at temperatures above about 2800.degree. F., and that the higher the temperature, the larger the amount of nitrogen oxides produced. Thus the production of oxides of nitrogen can be decreased by lowering combustion temperatures. Reducing temperatures of combustion in the combustion zone of a machine producing useful energy, however, will reduce its efficiency as well as its capacity for producing energy.
High combustion temperatures are undesirable because they require a design which provides for cooling mechanical components and increase the possibility of their failure through overheating. Further, when certain fuels are burned at a high temperature, undesirable products of combustion, such as slag, form to lower efficiency.